18.1 Content Negotiation (Eloquent JavaScript Solutions)

18-1 Eloquent Javascript Solutions.js

let aboutURL = 'https://eloquentjavascript.net/author';
let mediaTypes = [
  'text/plain',
  'text/html',
  'application/json',
  'application/rainbow+unicorns'
];

async function getResponsesForMediaType(url, type) {
  let r = await fetch(url, {headers: {'accept': type}});
  r = await r.text();
  console.log(`\n---------- type: ${type} ----------\n`, r);
};

for (let type of mediaTypes) {
  getResponsesForMediaType(aboutURL, type);
};

18.1 Content Negotiation

One of the things that HTTP can do is called content negotiation. The Accept request header is used to tell the server what type of document the client would like to get. Many servers ignore this header, but when a server knows of various ways to encode a resource, it can look at this header and send the one that the client prefers.

The URL eloquentjavascript.net/author is configured to respond with either plaintext, HTML, or JSON, depending on what the client asks for. These formats are identified by the standardized media types text/plain, text/html, and application/json.

Send requests to fetch all three formats of this resource. Use the headers property in the options object passed to fetch to set the header named Accept to the desired media type.

Finally, try asking for the media type application/rainbows+unicorns and see which status code that produces.

Hints

Base your code on the fetch examples earlier in the chapter.

Asking for a bogus media type will return a response with code 406, “Not acceptable”, which is the code a server should return when it can’t fulfil the Accept header.